docs: def coefficients(deriv, acc):
      """
      Calculates the finite difference coefficients for given derivative order and accuracy order.
      Assumes that the underlying grid is uniform. This function is available at the `findiff`
      package level.
      
      :param deriv: int > 0: The derivative order.
            
      :param acc:  even int > 0: The accuracy order. 
            
      :return: dict with the finite difference coefficients and corresponding offsets 
      """
  
      if acc % 2 == 1:
          acc += 1
  
      ret = {}
  
      # Determine central coefficients
  
      num_central = 2 * math.floor((deriv + 1) / 2) - 1 + acc
      num_side = num_central // 2
  
      ret["center"] = _calc_coef(num_side, num_side, deriv)
  
      # Determine forward coefficients
  
      if deriv % 2 == 0:
          num_coef = num_central + 1
      else:
          num_coef = num_central
  
      ret["forward"] = _calc_coef(0, num_coef - 1, deriv)
  
      # Determine backward coefficients
  
      ret["backward"] = _calc_coef(num_coef - 1, 0, deriv)
  
      return ret